Clarifiers are commonly used in many industries to separate an influent flow containing solids materials into an underflow sludge or solids component and a clarified liquid phase. Clarifier tanks conventionally comprise a tank bounded by a concave cross-sectioned floor and upstanding wall member which together form an enclosure within which the clarification occurs via sedimentation principles. Rotatable rake members or the like rotate to scrape underflow, thickened sludge from the floor to an underflow drain or discharge line while clarified liquid at the top of the clarifier tank flows over a weir or the like for collection.
In conventional clarifier tanks as described, an influent stream is introduced into the tank from a feedwell that is usually located in a central, upper portion of the tank. Introduction into the clarifier of an influent stream under conditions of high velocity variation and therefore higher peak flow velocities than desired tends to disturb or impede efficient settling of the liquor in the tank due to the turbulent action of the higher flow velocities on the settling solids particles.
Many of the existing clarifier feedwell designs include a number of features (separately or in combination) that contribute to uneven flow of the influent into the clarifier and therefore degrade clarifier performance. These features include:                1. Tangential feed flow to the feedwell (at the feedwell OD) with no provision to evenly distribute the flow either radially or circumferentially. This, in turn, leads to uneven flow into the clarifier. The tangential feed also adds relatively high levels of angular momentum to the clarifier which disrupts overall clarifier flow by “short-circuiting” the overall clarifier flow field with centrifugally driven radial (verses the desired axial—at this location of the clarifier) flow velocities.        2. Dual counter acting identical tangential feed streams which collide with one another within the feedwell. This “ideally” cancels angular momentum, but at the same time, exacerbates flow bias within the unit, so that overall flow improvement, in the clarifier ends up being minimal.        3. Relatively tall feedwell (and therefore feedwell feed) height for flow settling purposes in an attempt to compensate for 1 and 2 above. Consequently, when the clarifier is operated so that the liquor fluid surface is below this higher feed height, a “waterfall” is created from the feed level to the fluid surface level. This adds unwanted turbulence to the fluid which works against the quiescence in the flow required in the clarifier, and, at the same time, entrains air into the fluid (thus imparting additional upward flow to the fluid via the addition of more air bubbles) which, in turn, inhibits the downward movement of the solids to be settled.        